Importing Structure and Data - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 138

Limits for the transfer
When we import, the source file is usually on our client machine; so, it must travel to
the server via HTTP. This transfer takes time and uses resources that may be limited
in the web server's PHP configuration.

Instead of using HTTP, we can upload our file to the server using a protocol such
as FTP, as described in the Web Server Upload Directories section. This method
circumvents the web server's PHP upload limits.

Time limits
First, let's consider the time limit. In config.inc.php , the $cfg['ExecTimeLimit']
configuration directive assigns, by default, a maximum execution time of 300 seconds
(five minutes) for any phpMyAdmin script, including the scripts that process data
after the file has been uploaded. A value of 0 removes the limit, and in theory, gives
us infinite time to complete the import operation. If the PHP server is running in
safe mode, modifying $cfg['ExecTimeLimit'] will have no effect. This is because
the limits set in php.ini or in user-related web server configuration file (such as
.htaccess or virtual host configuration files) take precedence over this parameter.

Of course, the time it effectively takes depends on two key factors:

• Web server load

• MySQL server load

The time taken by the file, as it travels between the client and the server,
does not count as execution time because the PHP script only starts
to execute after the file has been received on the server. Therefore, the
$cfg['ExecTimeLimit'] parameter has an impact only on the time used
to process data (like decompression or sending it to the MySQL server).

Other limits
The system administrator can use the php.ini file or the web server's virtual host
configuration file to control uploads on the server.

The upload_max_filesize parameter specifies the upper limit or the maximum file
size that can be uploaded via HTTP. This one is obvious, but another less obvious
parameter is post_max_size . As HTTP uploading is done via the POST method, this
parameter may limit our transfers. For more details about the POST method, please
refer to http://en.wikipedia.org/wiki/Http#Request_methods .